Pressure response method for determining properties of species-dependent leakages in gas processing equipment

ABSTRACT

A system for building a gas processing apparatus includes a compressed gas source, a pressure modulator in communication with the gas source, and a chamber configured to receive a gas permeable material. The chamber is further configured with a first chamber area on one side of the material and with a second chamber area on a second side of the material. A sensor is configured to measure over time a pressure differential between the first and second chamber areas. A memory stores performance characteristic data for a plurality of gas processing apparatus. A processor converts the pressure differential to a material characteristic of the gas permeable material, and compares the material characteristic to at least one selected performance characteristic of the gas processing apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application which claims the priority to andbenefit of U.S. application Ser. No. 15/161,980 filed May 23, 2016 whichis incorporated herein in its entirety.

BACKGROUND OF THE INVENTION

The present invention generally relates to gas processing apparatus and,more particularly, to apparatus and methods of characterizing membranesand seals to build gas processing apparatus.

In devices such as equipment built for space programs where leakage ofgas is a prime consideration and may be gas species dependent—such asseals for a rotary distillation unit, or in applications wherespecies-dependent gas leakage is part of the designed function of theequipment such as in O2/N2 membrane separators—it is important to beable to characterize the relative leakage rate(s) as a function of theapplied pressures in a method that is independent from the normaloperating conditions of the equipment. The characterization can enableone to design and build a membrane and/or membrane module suitable foruse in the intended environments. The characterization can enable one todesign and build a membrane and/or membrane module suitable for use invarious environments.

In the absence of suitable characterization, one may be relegated toinstalling a membrane in a module, testing the module to see how themembrane performs, and then either using the membrane or discarding it.If the latter is needed, the process of installing another membrane andtesting will be required. In essence, one must go through atrial-and-error process to determine which membrane for a given moduleconstruction will work.

As can be seen, there is a need for improved apparatus and methods tocharacterize membranes and seals to build gas processing apparatus.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a system for building a gasprocessing apparatus comprises a compressed gas source; a pressuremodulator in communication with the gas source; a chamber configured toreceive a gas permeable material, wherein chamber is further configuredwith a first chamber area on one side of the material and with a secondchamber area on a second side of the material; a sensor configured tomeasure over time a pressure differential between the first and secondchamber areas; a memory that stores performance characteristic data fora plurality of gas processing apparatus; a processor that: converts thepressure differential to a material characteristic of the gas permeablematerial; and compares the material characteristic to at least oneselected performance characteristic of the gas processing apparatus.

In another aspect of the present invention, a method of characterizing amaterial comprises providing a chamber having a known volume; placingthe material in the chamber to create a first chamber area and a secondchamber area; inputting, over a time, an oscillating pressure into thefirst chamber area; measuring pressure, over the time, in the firstchamber area; measuring pressure, over the time, in the second chamberarea; determining, over the time, a pressure differential between thefirst chamber area and the second chamber area; wherein the pressuredifferential is based on at least one of a phase difference and anamplitude difference; and converting the pressure differential to amaterial characteristic; wherein the material characteristic is one of apermeance factor and a leakage rate constant.

In yet another aspect of the present invention, a method of building agas processing apparatus comprises providing a chamber; sequentiallyplacing different materials in the chamber to create a sequentialplurality of first chamber areas and second chamber areas; for eachmaterial and respective first chamber area and second chamber area:inputting, over a time, an oscillating pressure into the first chamberarea; measuring pressure, over the time, in the first chamber area;measuring pressure, over the time, in the second chamber area;determining, over the time, a pressure differential between the firstchamber area and the second chamber area; wherein the pressuredifferential is based on at least one of a phase difference and anamplitude difference; and converting the pressure differential to amaterial characteristic; wherein the material characteristic is one of apermeance factor and a leakage rate constant; and comparing at least oneof the material characteristics for the different materials to at leastone performance characteristic of the gas processing apparatus.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system for building a gas processing apparatus according toan embodiment of the present invention;

FIG. 2 is a graph of measured pressure according to an embodiment of thepresent invention;

FIG. 3 is a flow chart of a method of building a database according toan embodiment of the present invention;

FIG. 4 is a flow chart of a method of building a gas processingapparatus according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplatedmodes of carrying out the invention. The description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of the invention, since the scope of theinvention is best defined by the appended claims.

Various inventive features are described below that can each be usedindependently of one another or in combination with other features.However, any single inventive feature may not address any of theproblems discussed above or may only address one of the problemsdiscussed above. Further, one or more of the problems discussed abovemay not be fully addressed by any of the features described below.

Broadly, the present invention provides a method to characterizerelative leakage rates by response to a modulated, often sinusoidal,pressure acting through the unit under test while in communication to afixed volume. Based on the characterization, the present inventionprovides a method and apparatus to build a gas processing apparatus,such as an air separation module.

Generally, the present invention can be illustrated with an O2/N2 airseparation membrane module. The module inlet can communicate with anoscillating pressure source while the flow out of all outlets isblocked. A comparison can then made of the dynamic response of a shellside pressure to oscillations in a feed pressure. An amplitudeattenuation and a phase difference between the two oscillating pressuresare known functions of the frequency of oscillation and the totalleakage coefficient (or permeance) through the membrane. For feeds withmultiple gas species, correlations may be developed which map to speciespermeance and/or selectivity. Based on the permeance characteristics ofmultiple membranes, a database can be created and from which membrane(s)can be selected for building a membrane module having defined operatingcharacteristics.

FIG. 1 schematically depicts a system 10 for building a gas processingapparatus, such as an air separation module, according to an embodimentof the present invention. The system 10 may include a compressed gassource 11 a and external vacuum source 11 b in communication with apressure modulator 12 which, in combination, can provide a modulatingpressure 13, such as an oscillating pressure that may be in the form ofa sinusoidal wave.

The system 10 may further include a chamber 14 having a known volume andconfigured to hold therein a gas permeable material 17, such as amembrane or seal. The gas permeable material can divide the chamber 14into a first chamber area 15 and a second chamber area 16. The firstchamber area 15 can continuously or intermittently receive themodulating pressure 13 (or P1) over a period of time. Concurrently, thesecond chamber area 16 can receive over the period of time leakedpressure P coming from the first chamber area 14 and through the gaspermeable material 17.

FIG. 2 graphically depicts an exemplary measurement of P1 and P overtime. It can be seen that in this example the modulating pressure P1 ischaracterized by a sine wave 18. Also, in this example, the leakedpressure P is characterized by a sine wave 19 but the phase differs fromP1 (i.e., P has changed or shifted in time when compared to P1). In thisexample, P also differs from P1 in amplitude (i.e., P has changed ordecreased in amplitude when compared to P1).

Referring back to FIG. 1, a pressure sensor 20 in the system 10 maysense and measure, over the period of time, the pressures in the firstand second chamber areas 15, 16. The measured pressure data may bestored in a memory or database 21 of a computer.

A processor 22 may access the database 21 to convert the measuredpressure data to pressure differential data (e.g., phase shift and/oramplitude change). Then, the pressure differential data may be convertedto material characteristic data of the particular gas permeable material17 in the chamber 14. The latter may be, for example, permeancecharacteristic data and/or leakage rate characteristic data of the. Thematerial characteristic data can be stored in the database 21 or aseparate database.

In an exemplary embodiment, the conversion of pressure differential datamay be converted to material characteristic data as follows:

p ₁(t)=p ₀(γ+βsin(ωt))

Wherein p₁(t) is the characteristic of an applied pressure signal, wherep₀ represents initial pressure at equilibrium; p₀ (γ+β) represents themaximum instantaneous pressure; ω is the frequency of the appliedoscillation and β is the amplitude of the oscillation with theunderstanding that γ>0 and γ>β. A material balance over a control volumein the second chamber gives a closed form solution for the pressureexpected therein, which can be represented by the following equation:

${p\mspace{11mu} (t)} = {{p_{0}e^{{- \alpha}\; t}} + {\gamma \; {p_{0}\left( {1 - e^{{- \alpha}\; t}} \right)}} + {\frac{\beta\alpha\omega}{\alpha^{2} + \omega^{2}}{p_{0}\left\lbrack {{\frac{\alpha}{\omega}{\sin \left( {\omega \; t} \right)}} - {\cos \left( {\omega \; t} \right)} + e^{{- \alpha}\; t}} \right\rbrack}}}$

where α is the ratio of leakage flux to chamber pressure corrected fortemperature and chamber volume. When sufficient time has passed toestablish a stable oscillatory response, a stable phase shift isobservable and can be found to have the magnitude:

${{phase}\mspace{14mu} {shift}} \cong {\frac{1}{\omega}{{atan}\left( {\omega \text{/}\alpha} \right)}}$

Similarly, when a sufficient time has passed amplitude ratio can also beestablished:

${{amplitude}\mspace{14mu} {ratio}} \cong \frac{1 + \frac{\beta}{\gamma \sqrt{1 + \left( {\omega \text{/}\alpha} \right)^{2}}}}{1 + {\beta \text{/}\gamma}}$

Both phase shift and amplitude ratio are functions of a.

As depicted in FIG. 3, it can be appreciated that the present inventionprovides a method 30 of building, such as by the use of the system 10, adatabase 33 of material characteristic data, such as mass transfercoefficients, permeance and/or leakage rate characteristic data, for aplurality of gas permeable materials. In embodiments, a plurality of gaspermeable materials may be collected and/or created in a step 31,wherein the materials may differ from one another based on a combinationof different factors such as fiber geometry and fiber composition. Eachgas permeable material may then be characterized in a step 32, such asby permeance and/or leakage rate. All characterizations can then bestored in the database 33.

FIG. 4 depicts an exemplary method 40 for building a gas processingapparatus, such as an air separation module which can be, for example,an O2/N2 module. In a step 41, gas processing apparatus performancecharacteristic(s) may be added to the database 33 or to a separatedatabase. The performance characteristics can relate to how the gasprocessing apparatus is needed to perform for a particular application.Therefore, the apparatus performance characteristics may includeparameters such as gas flow rates, composition of gas streams, pressuredrops, etc.

In a step 42, at least one gas permeable material characteristic may becompared, such as by the processor 22, to at least one selected gaspermeable apparatus performance characteristic. Based on comparativesimilarity(s), a computer simulated gas processing apparatus can bedesigned, such as by the processor 22. The design parameters can includeparameters such as interfacial area, maximum and minimum workingpressures, equipment geometry, and other application specificparameters.

In a step 43, the computer simulated apparatus design may undergocomputer simulated operation, such as by the processor 22, during, forexample, steady-state operation.

In a step 44, it can be determined, such as by the processor 22, whetherthe simulated operation met at least one of the apparatus performancecharacteristics. If “no”, then the method 40 can return to step 42. If“yes”, then the method can proceed to a step 45.

In a step 45, it can be determined, such as by the processor 22, whetherthe computer designed apparatus should be optimized. If “yes”, then themethod 40 can return to step 42. If “no”, then the computer designedapparatus is converted, such as by the processor 22, into a final designof an actual gas processing apparatus.

It should be understood, of course, that the foregoing relates toexemplary embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

We claim:
 1. A system for building a gas processing apparatus,comprising: a compressed gas source; a pressure modulator incommunication with the gas source; a chamber configured to receive a gaspermeable material, wherein chamber is further configured with a firstchamber area on one side of the material and with a second chamber areaon a second side of the material; a sensor configured to measure overtime a pressure differential between the first and second chamber areas;a memory that stores performance characteristic data for a plurality ofgas processing apparatus; a processor that: converts the pressuredifferential to a material characteristic of the gas permeable material;and compares the material characteristic to at least one selectedperformance characteristic of the gas processing apparatus.
 2. Thesystem of claim 1, wherein the pressure modulator provides anoscillating pressure.
 3. The system of claim 1, wherein the chamber isof a known volume.
 4. The system of claim 1, wherein a pressure in thefirst chamber area is characterized by a sine wave.
 5. The system ofclaim 1, wherein a pressure in the second chamber area is characterizedby a sine wave.
 6. The system of claim 1, wherein the pressuredifferential is a phase difference.
 7. The system of claim 1, whereinthe pressure differential is an amplitude difference.
 8. The system ofclaim 1, wherein the pressure differential is a phase difference and anamplitude difference.
 9. A method of characterizing a material,comprising: providing a chamber; placing the material in the chamber tocreate a first chamber area and a second chamber area; inputting, over atime, an oscillating pressure into the first chamber area; measuringpressure, over the time, in the first chamber area; measuring pressure,over the time, in the second chamber area; determining, over the time, apressure differential between the first chamber area and the secondchamber area; wherein the pressure differential is based on at least oneof a phase difference and an amplitude difference; and converting thepressure differential to a material characteristic; wherein the materialcharacteristic is one of a permeance factor and a leakage rate constant.10. The method of claim 9, wherein the measured pressure in the firstchamber area is characterized by a sine wave.
 11. The method of claim 9,wherein the measured pressure in the second chamber area ischaracterized by a sine wave.
 12. The method of claim 9, wherein thepressure differential is based on both the phase difference and theamplitude difference.
 13. The method of claim 9, wherein the material isa gas permeable membrane.
 14. The method of claim 9, wherein thematerial is a seal.